1. Field of the Invention
This invention relates to pharmaceutical excipients, and, more particularly, to a proliferous copolymer of vinyl pyrrolidone and vinyl acetate having advantageous dissolution and disintegration properties.
2. Description of the Prior Art
Zhong, Y. et al, in U.S. Pat. No. 5,663,258, described a strongly swellable, moderately crosslinked copolymer of vinyl pyrrolidone and vinyl acetate made by precipitation polymerization in the presence of a free radical initiator. The copolymer obtained by this process had unique gel volume and viscosity properties which enabled it to thicken aqueous and non-aqueous solutions effectively.
Meffert, H., in EP 0979649A2, also described copolymers of vinyl pyrrolidone and vinyl acetate made by free radical polymerization, optionally with an added crosslinking agent, which process provided copolymers having K-value of 50 to 200. Such copolymers were considered suitable for use as a matrix material in pharmaceutical or cosmetic preparations.
Blankenburg, R. et al, in U.S. Pat. No. 5,635,169, also described a free radical process for making copolymers of vinyl pyrrolidone and vinyl acetate having a K-value of 30-50 for use in cosmetic formulations.
Tseng, S. et al, in U.S. Pat. No. 5,393,854, described the preparation of the isomeric compound 1-vinyl-3(E)-ethylidene pyrrolidone (EVP) having the formula: 
which, in solid form, had a purity of at least 95% and were white, needle-shaped crystals having a melting point of 59-61xc2x0 C. This isomeric compound was used as a crosslinking agent in the proliferous polymerization of vinyl pyrrolidone.
Tseng, S. et al in U.S. Pat. No. 5,393,854, also described a polymerizable composition of vinyl pyrrolidone and isomeric EVP for proliferous polymerization of vinyl pyrrolidone.
Accordingly, it is an object of the present invention to provide a proliferous copolymer of vinyl pyrrolidone and vinyl acetate for use as efficient excipient for drugs, and which has advantageous dissolution and disintegration properties at predetermined pH levels. No free radical initiators are employed in the present invention.
What is described herein are pharmaceutical excipients which are proliferous copolymers of vinyl pyrrolidone (VP) and vinyl acetate (VA) having more advantageous dissolution and disintegration properties than proliferous polyvinylpyrrolidone itself, or of soluble or swellable copolymers of vinyl pyrrolidone and vinyl acetate, made by a free radical process. The invention also includes a process for making such proliferous copolymers, and excipient tablets of a drug and such copolymers. In particular, the proliferous copolymers of vinyl pyrrolidone and vinyl acetate of the invention exhibit slower dissolution and disintegration properties under aqueous acidic conditions (which is attributed to their increased hydrophobicity) as compared to polyvinylpyrrolidone homopolymer.
Specifically, a proliferous copolymer of the invention, consists essentially of, by weight, about 60-85% VP, about 1540% VA, and about 1-5% of a crosslinker.
The proliferous polymerization process for making the proliferous copolymer of the invention comprises providing a polymerization mixture of, by weight, 60-85% VP, 15-40% VA, and about 1-5% crosslinker, at a temperature of about 100xc2x0 C., heating until proliferous polymerization occurs, and then recovering the desired copolymer.